Classically, time-varying magnetic gradients are generated for use in MRI by applying currents to coils that are in the vicinity of a sample to be imaged. As a result of the large inductance of the coils, substantial energy is required to initialize the flow of these currents through the coils. If the magnetic gradients are rapidly activated, the voltage required to initiate current in the gradient coils can be high, leading to high voltage-handling requirements. Some of the current flowing through the gradient coils is wasted in the form of heat, which can deleteriously raise the temperature in nearby components or decrease the current flowing in the gradient coils. Additionally, the currents in the activated gradient coils can couple to other nearby coils. This coupling of nearby coils can heat those nearby coils, introduce unwanted gradient fields, or introduce additional radiofrequency (RF) noise.
As described in earlier patent applications by inventor Weinberg (application Ser. No. 13/439,382), it is possible to use fast MRI to image teeth or other solid objects. The free-induction decay (FID) of protons in teeth is rapid (T2<50 microseconds), so in order to apply spatial localization pulses, the gradient fields must be rapidly applied. Traditional methods of gradient field applications would necessitate large power supplies capable of delivering significant currents in small intervals. In order to image teeth cost-effectively with MRI, it is preferable to minimize the power requirements of gradient coil activation.